[time-nuts] AN/URQ13 reference AT cut crystal?

[Magnus Danielson]

Hi Paul,

On 2021-02-17 15:38, paul swed wrote:
> Bob
> I thought SC's were around a long time. (Not that I doubt you on that) This
> thing should be the 1970s vintage from the one bit I have found on it.
Research-wise, you come back to about 1974 it seems. Production seems to
start at about 1981.
> Magnus always appreciate your comments.
Uhm, I did not know that my appreciation for someones comments was used
as a hallmark for quality. I sit here in amazement of what just happen.
Bob has delivered insight from so many decades in the industry, and that
insight shows of in quality of posts, that is always appreciated.
> As I heat it up from room temperature what exactly would I look for? Sort of the
> temperature/frequency behaviors I see in various charts?
> When cold the units sit 4Hz high. and when warm its currently .119 Hz high.
> It used to go below by .6 Hz. Not sure what has changed.

So, as you heat up from 20 C to 85 C the frequency shift. Depending on
cut, the start offset (cold frequency - nominal frequency) have
different sign and size, depending on cut. It's fairly easy to spot
different cuts that way we concluded.

You can dig up frequency error vs. temperature graphs for various cuts.
The AT-cut one is well spread third degree shape going up to a
saddle-point, going down to a saddle-point and then going up again.
Minimum sensitivity to temperature happens on those saddle-points.

I remembered a setup where someone used SC-cut oscillators in cryogenic
temperature setup to detect axions. He noted that they where fighting
temperature variations to the oscillators. I simply asked if the SC-cut
crystals had been cut for that temperature, and apparently not. Well,
there is a basic magic to the stability, and if you do not respect that
magic, do not expect the result to be so spectacular either. That said
from someone who have yet to design a single crystal oscillator beyond
following standard datasheet setup.

The Gerber & Ballato "Precision Frequency Control" books is a good read.
Chapter 12 by Sam Stein I know exists as separate PDF, maybe other parts
too. It has tabulated coefficients for AT, BT, IT and SC cuts cubic
temperature dependence.

Cheers,
Magnus